Speculative investment would be someone buying Bitcoin for the explicit purpose of trying to get more value out than they put in when they trade later on. A store of value usage would be if someone just wanted to preserve their wealth, so they buy Bitcoin with intent to trade for similar value without the intention of relative appreciation of Bitcoin relative to other assets.
But there is absolutely no guarantee your wealth will be preserved with Bitcoin or any other investment instrument.
When you say, "investment XYZ will preserve my wealth", you are speculating that is the case since, not being God, you cannot predict the future.
No matter what, you are predicting the future: you are speculating on the future value of Bitcoin (or whatever investment). This is true for US dollars as well (if you choose not to decide you still have made a choice, etc.).
There really isn't. Any professional investor views them as exactly the same, because they are.
For instance, perhaps many here believe that Bitcoin will preserve your wealth forever and ever--it will maintain its value or increase no matter what. Other people would point out that Bitcoin's value is extremely volatile and has dropped in value by 80% in the recent past, and may drop again and stay that way.
Some of those people may be right, and some of them may be wrong. Only God knows who. But both are speculating.